Currently, searches for sterile neutrinos with displaced vertex signature have been performed at LHC [1]}, [2]}, [3]}. The exclusion limit could reach \(m_N\lesssim 15\)  GeV and \(\theta ^2\gtrsim 3.6\times 10^{-7}\)  [2]}. In the future, several experiments such as SHiP [5]}, [6]}, CEPC [7]}, LHC [8]}, [9]} and FCC-hh [10]} could detect the parameter space with \(m_N\lesssim m_W\)  and \(\theta ^2\gtrsim 10^{-11}\) . These limits can be found in Fig. REF , however, none of them could reach the theoretical seesaw limit [11]}.
